50 Concrete in Australia Vol 39 No 2
FEATURE: BRIDGES
of the bridge required the use of an extensive design review
and management process throughout the project. Australian
Standards 1 were used in the design with durability the main
focus. e superstructure was modelled in two dimensional
grillages, due to the staged construction of the bridge,
following generally accepted methods outlined by Hambly 2.
e first grillage modelled the aqueduct segments during the
launching process and the second modelled the entire bridge
for the permanent condition. e aqueduct was designed for
T44 maintenance truck. An allowance of 12 mm differential
settlement between supports was also considered in design.
At permanent stage, the aqueduct (half symmetric) was
modelled using Strand 7, a 3D finite element software,
with concrete as "brick" elements to check the stresses of
the anchorage zone (Figure 3). e finite element model
enabled aqueduct reinforcement to be detailed for the tensile
stresses identified at the anchorage zone, as shown in Figure
4. e maximum shear at the 12 m cantilever and the tensile
stresses developed at the anchorage zone required extensive
reinforcement at the bridge ends to comply with both the
strength and serviceability criteria specified in AS 5100.5.
Arranging this reinforcement within the 300 mm web was
difficult. However, careful detailing and the use of couplers
enabled the successful integration of the final layout of the
reinforcement within the aqueduct, as shown in Figure 5.
4.2 HDPE Liner
A major challenge for the aqueduct was the concrete durability
given the aggressive environment within the sewer pipe.
e latest technology for sewer protection was investigated
by the project team to ensure the long term durability of
the structure. An HDPE anchored liner proved to be the
most effective system and was more resistant to hydrogen
sulphide (H2S) than other options. e comparatively new
lining system involved mechanical bonding with the concrete
through conical anchor studs on the rear of the liner. e
5 mm thick lining sheets were placed on the internal
formwork upside down and cast in with the concrete.
International standards and codes were used in the design
and specification of HDPE liner.
Casting the liner into the aqueduct presented challenges,
including:
• Adequate restraint to movement as temperature varied
around it.
Figure 2. Tendon coupler at the end of the segment.
Figure 3. Strand 7 model of half bridge.
Figure 4. Strand 7 output -- anchorage.